Methods of and apparatus for identifying articles, e. g. in an automatically controlled system

ABSTRACT

Apparatus for sensing identifying markings on articles, consisting of markers of two kinds, magnetic and nonmagnetic, selected to represent a binary number (the two kinds of marker corresponding to the digits 0 and 1) comprises one or more electromagnetic sensing devices, each device having a magnetic circuit into which a marker can be placed to produce an electric output governed by the reluctance of the magnetic circuit.

United States Patent lnve ntors David Theodore Nelson Williamson;

Douglas William Ballantyne Muir; Richard Graham Grosland; Edward HenryParke, all of Depttord, England Appl. No. 759,740

Filed Sept. 13, 1968 Patented July 20, 1971 Assignee Molins MachineCompany Limited London, England Priority Sept. 13, 1967 Great Britain41,870/67 METHODS OF AND APPARATUS FOR IDENTIFYING ARTICLES, E. C. IN ANAUTOMATICALLY CONTROLLED SYSTEM 3 Claims, 4 Drawing Figs.

[1.5. CI ...235/6l.llD Int. Cl 606k 7/08 FieldofSearch 235/6111,

61.11 D; 340/174.1 H, 174.1 R, 1741A, 174 AG References Cited UNITEDSTATES PATENTS 2,908,278 10/1959 Goerlich 235/61.11 UX 3,210,527 10/1965Daykin 235/61.11 3,215,820 11/1965 Heard, Jr 235/61. 3,317,714 5/1967Hausler etal 235/61.11

Primary ExaminerDary1 W. Cook AttorneysEmory L. Groff and Emory L.Groff, Jr.

ABSTRACT: Apparatus for sensing identifying markings on articles,consisting of markers of two kinds, magnetic and nonmagnetic, selectedto represent a binary number (the two kinds of marker corresponding tothe digits 0 and 1) comprises one or more electromagnetic sensingdevices, each device having a magnetic circuit into which a marker canbe placed to produce an electric output governed by the reluctance ofthe magnetic circuit.

PATENTED JUL20 :97:

SHEET 1 [IF 3 PATENTEU JULZO I97i SHEET 2 BF 3 METHODS OF AND APPARATUSFOR IDENTIFYING ARTICLES, E. G. IN AN AUTOMATICALLY CONTROLLED SYSTEMThis invention relates to apparatus for sensing identifying markings onarticles. Apparatus embodying the invention may be used for a variety ofpurposes, but one preferred use of such apparatus is in acomputer-controlled machine tool system.

It should be noted that while in this specification reference is made tothe use ofbinary numbers for identifying articles, it should beunderstood that this does not limit the invention to use where purelynumerical identification is employed, as of course any form ofidentification may be used provided that it is represented in abinary-coded form (i.e. using only two symbols, conventionally O and lAlso, references hereafter to magnetic" and nonmagnetic materials arenot intended to refer to materials which are respectively magnetized andnot magnetized, but rather to materials which do or do not haveferromagnetic properties.

According to the invention, there is provided apparatus for sensingidentifying markings on articles constituted by combinations of markersof two kinds, viz of magnetic and nonmagnetic material, carried by eacharticle at predetermined positions to represent a binary number. Amarker of one kind represents the digit 1 and a marker of the other kindrepresents the digit 0, said apparatus comprising at least oneelectromagnetic sensing device having a magnetic circuit into which oneof said markers can be placed and to produce an electric output governedby the reluctance of the magnetic circuit.

Preferably, the apparatus has a plurality of sensing devices, inpredetermined positions complementary to the arrangement of markers oneach article, so that when an article is brought to the sensingapparatus each marker is brought into the magnetic circuit of adifferent one of the sensing devices; all the digits of the binarynumber represented by the markers on the article are then simultaneouslyindicated by the electric output from all the sensing devices, i.e. thenumber is read" from the article in the parallel mode. However, ifdesired, a single sensing device may be used, and in that event means isprovided for moving each article past said device so that the markerspass into and out of its magnetic circuit in sequence; the electricoutput of the device during the time the markers are passing through themagnetic circuit then constitutes a readout of the binary number in theserial mode. (A serial readout may also be obtained, of course, bymoving a single sensing device relative to a stationary article.)

Conveniently, each sensing device includes a coil coupled to themagnetic circuit. As the reluctance of the magnetic circuit will belower when a marker placed in the circuit is of magnetic material thanwhen such marker is of nonmagnetic material, the inductance of the coilwill be higher in the first instance than in the second. This differencemay readily be made to produce different electric output signals; in apreferred arrangement, the coil is connected in a circuit to beenergized by an alternating voltage applied through a series resistor,so that when the coils inductance is high (because a marker of magneticmaterial is in the magnetic circuit) the alternating voltage across thecoil is greater than when its inductance is low (because a marker ofnonmagnetic material is in the magnetic circuit). The AC output may berectified and the resulting DC signal amplified so that a final outputis obtained in which two different DC voltage levels represent thedigits 0 and l for many applications it is convenient for one of said DCvoltage levels to be zero. Preferably the apparatus includes means forproducing a reference voltage and means for deriving the differencebetween the output from the coil and the reference voltage as the finaloutput voltage. Such a reference voltage may advantageously be producedby a further device generally similar to the sensing device(s) but whichis so arranged that during operation of the apparatus the further deviceis always in a condition substantially the same as that of the sensingdevice when a selected one of the two kinds of marker is in its magneticcircuit. This effect may be achieved either by suitable housing of thefurther device or (where a plurality of sensing devices are provided forparallel readout) by treating the further device as an additionalsensing device but providing each article with a reference marker forsensing by the further device, the reference markers of all the articlesbeing'markers of the same kind.

Apparatus in accordance with the invention will now be described, by wayof example, with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of apparatus for reading a binary numberrepresented on an article which is shown in broken line,

FIG. 2 is a sectional view through the apparatus and the article shownin FIG. 1;

FIG. 3 is a circuit diagram illustrating the electrical connections andcomponents used with the apparatus shown in FIGS. 1 and 2; and

FIG. 4 is a diagram of a modified form of apparatus, incorporating ashift register and giving both serial output and parallel output.

Referring first to FIGS. 1 and 2 the apparatus comprises a blocklikesupport member 11 made of magnetic material, and in the present instanceof mild steel. Housed in the block 11 are electromagnetic detectordevices generally indicated by the reference 12 in FIG. 1. Each detectordevice 12 comprises, as can be seen from FIG. 2, a detector coil 13wound on a bobbin having a core 14 of magnetic material, around whichthe coil is wound, and end caps 15. The detector devices 12 are arrangedat spaced positions along the block 11 with one end of each core 14exposed and in line with the forward face of the block I! as viewed inFIG. 1. It will be understood that each detector coil 13 is coupled to amagnetic circuit through its associated core 14 and through thesurrounding material of the block 11, but having an airgap at theexposed end, i.e. at the surface of the member 11. If magnetic materialis placed close to the surface of the member 11 so that the material isinterposed in the magnetic circuit, the reluctance of the magneticcircuit is less than when no such material is present. This effect onthe magnetic circuit can be utilized to detect the presence or absenceof magnetic material adjacent the exposed end of the core 14 of adetector device.

As explained later, each detector coil 13 is arranged in an electricalcircuit so that an alternating electric current is passed through thecoil to establish an alternating magnetic field (i.e. to create andcollapse magnetic fields of opposite polarity in alternation) in itsmagnetic circuit, and so that the reduction in reluctance (causing anincrease in the inductance of the coil) which occurs when additionalmagnetic material is interposed in the magnetic circuit is apparent asan increase in output voltage across the coil.

A binary number can be represented on an article by markers of twokinds, i.e. of magnetic material and of nonmagnetic material, at spacedpositions, each marker representing one bit" of the number. Each markerof magnetic material represents one of the two digits 1 and 0, e.g. l,and each marker of nonmagnetic material represents the other of the twodigits 1 and 0, e.g. 0. An article 16 having a binary number sorepresented on it is shown in FIG. 2. The article has holes at spacedpositions along one face, the spacing between the holes corresponding tothat between the detector devices 12 in the block 11, and each hole isfilled either with a plug 17 of magnetic material representing the digit1, or with a plug 18 of nonmagnetic material representing the digit 0.Thus that part of the particular binary number represented on thearticle 16 shown in FIG. 2 reads, from left to right, I lOlOO I.

If the article 16 is positioned in closely adjacent relationship to theblock 11 as shown in FIG. 2 so that the plugged holes in the articleregister with the detector devices 12 in the block, each detector device12 can detect whether its registering plug is of magnetic material, i.e.is a plug [7, or is of nonmagnetic material, i.e. is a plug 18. Eachdetector device registering with a plug 17 will have the reluctance ofits magnetic circuit reduced, thereby distinguishing it from themagnetic circuits of the detector devices registering with plugs 18. Inthis manner the detector devices in the block 11 effectively read thebinary number on the article, and, in a manner described later, theapparatus can emit a signal controlled by the magnetic circuits of thedetector devices to be representative of the binary number.

It will be appreciated that various other forms of representation of thebinary number on the article can be used instead of the insertion ofplugs of magnetic and nonmagnetic material as described above. Forexample, if the article, or an appropriate part of the article, isitself of a magnetic material, holes can be made at those positions(e.g. representing the digit where such material is not required, andthe material of the article itself can provide the magnetic requirementof the other positions (e.g. representing the digit 1). The holes canthen either be plugged with material of low magnetic permeability or, ifpreferred, left open. Conversely, if the article, or an appropriate partof the article, is of a nonmagnetic material, the number can berepresented by making holes and inserting plugs of magnetic material atthose positions where such material is required to represent one digit(e.g. I), the other positions representing the other digit (e.g. 0)being occupied by the material of the article. As a further example,whatever the material of the article, the number can be applied theretoby affixing a suitable strip having the appropriate arrangement of holesand/or plugs, eg a strip of magnetic material having holes, which may ormay not be plugged with nonmagnetic material, at the required positions,or a strip of nonmagnetic material with plugs of magnetic material inholes at the desired positions. Still further, the article could beprovided with or have affixed thereto projecting plugs of magneticmaterial at the appropriate positions which represent one of the twodigits.

The apparatus can advantageously be used in an automatically controlledsystem in which a plurality of articles are used and transported, and itis required to identify an article at a location in the system. Each ofthe articles can be provided with an identifying binary numberrepresented on the article in a manner as described above, and theapparatus can be arranged at the desired location so that, when anarticle is positioned at that location with its binary number oppositethe member 11 as shown in FIGS. 1 and 2, the number can be read and thearticle identified. In particular, the apparatus is suita ble for use ina computer-controlled machine tool system as described in theaforementioned application in which pallets, on to which workpieces areloaded for machining, are transported, the pallets bearing identifyingbinary numbers, and their numbers being read at various locations in thesystem. The article 16 shown in FIGS. 1 and 2 is a pallet, having adatum block 19 at one comer, as described in the aforementionedapplication. In the system described in that application tool magazines,tape cassettes, and bins are also provided with identifying binarynumbers which are required to be read at various locations in thesystem, and the apparatus described herein is suitable for identifyingthese articles also.

FIG. 3 illustrates the electrical circuitry by which the effect producedon the detector devices 12 is translated into a signal representative ofthe binary number being read. The apparatus includes an electromagneticreference device which is not shown in FIGS. 1 and 2 but which isessentially identical to each of the detector devices 12 and has acentral core of magnetic material around which is wound a reference coilindicated as RC in FIG. 3. The reference device is housed so that thereluctance of the magnetic circuit produced by energizing the referencecoil is in operation always substantially equivalent to that of themagnetic circuit of a detector device 12 when the latter is adjacent aplug 18 of nonmagnetic material. To achieve this, the reference devicemay, if desired, be housed in the block 11 in exactly the same way asthe detector devices 12, the articles whose binary numbers are to beread all being provided with a plug 18 of nonmagnetic material at aposition which registers with the reference device when reading occurs,i.e. when the article 16 and block 11 are in the positional relationshipshown in FIGS. 1 and 2. In this manner the magnetic circuit ofthereference device is substantially the same as that of the detectordevices facing a plug 18 (which represents the digit 0) and the magneticcircuits of the detector devices facing a plug 17 (of magnetic materialand representing the digit 1) can be distinguished by comparison withthe magnetic circuit of the reference device.

An alternating input voltage is applied across the reference coil RC anda resistor R1 arranged in series therewith. The alternating outputvoltage across the reference coil RC alone is rectified by means ofadiode D1 with a resistance-capacitance load provided by a resistor R2 inparallel with a capacitor C1, and is applied to the base of a PNP-typetransistor T1 whose collector has a negative voltage --V2 appliedthereto. The emitter of the transistor T1 connects with the base ofafurther transistor T2 to whose collector a negative voltage V2 is alsoapplied, the transistors T1 and T2 being Darlington-connected emitterfollowers. The emitter of the transistor T2 is loaded with a resistor R3and connects with a reference line RL.

Each detector coil 13, of which one indicated as DC1 is shown at thebottom left-hand corner of FIG. 3, has the input alternating voltage V1applied across the coil and a resistor R4 arranged in series therewith.The alternating output voltage across the detector coil alone isrectified by means of a diode D2 with a resistance-capacitance loadprovided by a resistor R5 in parallel with a capacitor C2, and isapplied to the base of an NPN-type transistor T3 whose collector has apositive voltage +V2 applied thereto. The emitter of the transistor T3connects, through a resistor R6, with a junction J. One line from thejunction J connects, through a resistor R7, with the reference line RL,and the other line connects with the base of an NPN-type outputtransistor T4 whose emitter is grounded. A positive voltage of +V2 isapplied through a resistor R8 to the collector of the transistor T4,which also connects with a signal line SL1 across a load resistor R9.

When a binary number is read by the apparatus in the manner explainedabove, the output voltage across the detcctor coil is dependent uponwhether the detector device is opposite a plug 17 of magnetic materialor a plug 18 of nonmagnetic material. If the detector device is oppositea plug 17 of magnetic material which decreases the reluctance of themagnetic circuit thereby increasing the inductance of the detector coil,the output voltage across the coil will be greater than that when thedetector device is opposite a plug 18 of nonmagnetic material (when themagnetic circuit will have a greater reluctance and the coil will have alower inductance). The output voltage across the detector coil isrectified, as described above, and applied to the base of the transistorT3 whose output is fed to the junction J, which acts as a Kirchhoffadder, by means of which the output voltage across the detector coil DC]can be compared with the output voltage across the reference coil RC.

As is apparent from the circuits shown in FIG. 3, the reference voltageapplied to the reference line RL representative of the output voltageacross the reference coil RC is of the opposite polarity to the detectedvoltage from the detector coil. Thus, if the reference voltagesubstantially equals the detected voltage the current flow through theresistors R6 and R7 via the junction .I will be substantially equal, andthe voltage at junction J will be such that the output transistor T4 iseffectively cut off. If, on the other hand, the detected voltage exceedsthe reference voltage, the voltage applied to the base of the outputtransistor T4, which connects with the junction J, will cause a signalvoltage to be established on the signal line SL1.

Preferably, the reference voltage is arranged to be greater in magnitudethan the detected voltage when the detector device is opposite a plug 18of nonmagnetic material, for example by about 20 percent, so that asignal on the line SL1 is only established when the detector device isopposite magnetic material provided by a plug 17 and the detectedvoltage is considerably greater, e.g. by more than the 20 percent, thanthat occurring when the detector device is opposite a plug 18 ofnonmagnetic material.

In the particular embodiment described the voltage and component valuesare as follows:

V,=50 v. R.M.S.

RS =l00 K R9 is of a value selected to reduce the output on the signalline to a required voltage level Cl =2.2 f, 35 v.

C2 =2.2 p.f., 35 v. RC Identical coils of 6000 turns D01 The transistorsT1 and T1 are identical, as are the transistors T3 and T4; T1 and T2 mayeach be of type 2N3702, and T3, T4 may each be of type 2N3704, althoughthe actual types of transistor used is not important in theseemitter-follower circuits. The resistors and inductance reference anddetector coils may have a 12 percent tolerance. The detector devicecores 14 are 3 mm. in diameter and the plugs 17 and 18 have a 10 mm.diameter, the pitch of the plugs and detector devices being 14 mm.

By this arrangement a voltage swing of 10 volts can be detected asbetween a detector device opposite a plug 17 of magnetic material and adetector device opposite a plug 18 of nonmagnetic material when a gap ofone-thousandth of an inch is left between the plug and the detector core14. If this gap is increased to fifteen-thousandths of an inch thevoltage swing is reduced to 4 volts. The materials of the plugs 17 and18 are a suitable ferrous material, such as cast iron, and a suitablenonferrous material, such as plastic, respectively. However, asexplained previously,if the article 16 is itself of magnetic material,such as cast iron, unplugged holes can be provided at those positionscorresponding to the plugs 18, so that a detector device opposite such aposition is opposite air, and the material of the article can serve thepurpose of the plugs 17.

It will be appreciated that a detector circuit as described above, i.e.comprising the components R4, R5, R6, R7, R8, R9, D2, C2, T3 and T4 isprovided in association with each detector coil, the input voltage V1being applied across each detector coil and its series resistor R4 froman input voltage line IVL, and each detector circuit having its resistorR7, connected to the reference line RL, i.e. the detector circuits arearranged in parallel along the lines IVL and RL. In the particularembodiment described there are detector devices 12 and hence l5 detectorcircuits, but for convenience FIG. 3 shows only two detector circuits,one associated with the first detector coil DC] and the other associatedwith the 15th detector coil DCl5.

Signal lines SL1 to SLIS emanate from the detector circuits and when abinary number is being read a signal is established on each signal linewhose detector device is opposite a plug 17 of magnetic material in themanner described above. The signal lines SLI to SL15 therefore togethercarry a signal representative of the binary number being read, whichsignal can be communicated to control means controlling the system inwhich the apparatus is being used, thereby identifying the article whosenumber is being read to the control means. Thus, in particular, if theapparatus is used in a computer-controlled machine tool system asdescribed in the aforementioned application, the signal lines SL1 toSL15 can be constituted by, or connect with, the Data" lines describedin that application.

It will be appreciated that the number of detector devices and signallines, which is 15 in the described embodiment, can be chosen to meetrequirements. The 15 devices described enables a l5-bit" binary numberto be read, which may, in practice, be made up ofa l2-bit binary numberand three bits" used to provide a check, e.g. a Modulus Seven check.

FIG. 4 illustrates diagrammatically a modified apparatus embodying theinvention which is capable of reading a binary number represented on amoving article and producing both a serial and a parallel electricaloutput representing such number. The article 16 (as in FIGS. 1 and 2)with its l5 plugs 17, 18 (FIG. 2) contained in the shaded region 16a,moves past a stationary sensing unit A containing the electricalcircuitry shown in FIG. 3 within a dashed-line enclosure also marked A.In particular, this unit includes the detector coil DC] and as indicatedin FIG. 4 this component is so placed in the unit A as to be confrontedby the plugs 17, I8 in sequence as the movement of article 16 carriesthem past the unit A.

The signal line SL1 will accordingly carry a voltage which at anyinstant that one of the plugs l7, 18 is aligned with the coil DCl willindicate whether that plug is one of the plugs 17 (i.e. is of magneticmaterial, representing the digit 1) or one of the plugs 18 (ofnonmagnetic material, representing the digit 0). The signal line SL1 isconnected to a shift register R, and at each instant a plug is alignedwith coil DCl, a functional input F of said register is impulsed tocause a right shift in the register, causing the first (left-hand)bistable stage of the register to be set to the condition (i.e. torepresent 0 or I) corresponding to the voltage on line SL1, while thesecond stage assumes the condition previously sustained by the firststage, and so on; in short, the first stage goes to a conditioncorresponding to the type of plug then aligned with the coil DCI, whilesimilar digital indications stored during the passage of previous plugspast the coil DCl are each shifted one place to the right. The registerR has 15 stages (equal to the number of binary digits represented by theplugs) and (whatever the initial state of the register) when the 15plugs of article 16 have moved past coil DC], the register will contain,in correct sequence, stored indications of the binary digits representedby the plugs l7, 18 of that article.

A further l5 impulses applied to the input F, while a zerorepresentingvoltage is maintained on line SL1, will cause the register R to shiftanother 15 times to the right, delivering on a serial output line S asequence of pulses representing the stored binary digits and clearingthe register R. While the register R contains the stored indications ofall 15 digits, however, these digits may be read out simultaneously on aset of parallel output lines P (whether this clears the register or notdepends upon the internal structure of the register).

' It will be apparent that the apparatus of FIG. 4 can only operaterelatively slowly as the digital indications derived from the plugs l7,18 of an article 16 are being stored, as the speed at which the registerR can be operated depends upon the speed of travel of the article. Onceall the digital indications are in storage, however, the register can beread out (either in the parallel or the series mode) at much greaterspeed. The register R may if desired be of such form that each numberstored can be read out in both modes and/or repeatedly read out ineither mode.

What we claim as our invention and desire to secure by Letters Patentis:

1. Apparatus for sensing article-identifying markings constituted bycombinations of markers of two kinds, viz of magnetic and nonmagneticmaterial, carried by each article at predetermined positions torepresent a binary number, a marker of one kind representing the digit 1and a marker of the other kind representing the digit 0, said apparatuscomprising at least one electromagnetic sensing device including amagnetic circuit into which one of said markers can be placed to producean electric output governed by the reluctance of said magnetic circuit,each said sensing device including a coil coupled to the magneticcircuit, means for producing a reference voltage and means for derivingthe difference between the output from the coil and said referencevoltage as the final output voltage.

2. Apparatus as claimed in claim 1, in which the means for producing thereference voltage comprises a further device including a magneticcircuit having a reluctance which is always in a condition substantiallythe same as that of the sensing device when a selected kind of marker isin its magnetic circuit.

3. Apparatus for sensing article-identifying markings constituted bycombinations of markers of two kinds, viz of magnetic and nonmagneticmaterial, carried by each article at predetermined positions torepresent a binary number, a marker of one kind representing the digit 1and a marker of the other kind representing the digit 0, said apparatuscomprising an electromagnetic sensing device including a magneticcircuit into which one of said markers can be placed to produce anelectric output governed by the reluctance of said magnetic circuit,means for moving each article past said sensing device so that themarkers therein pass into and out of the magnetic circuit of the devicein sequence to produce an output signal comprising a series of pulses ona single output line, said single output line connected to deliver saidpulses to a shift register so that after all said markers have passedinto and out of the magnetic circuit said shaft register contains astored representation of the binary number represented by said markers,said shift register being operable to read out said storedrepresentation in the serial or the parallel mode.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 I 550Dated July 1971- Inventods) David Theodore Nelson Williamson t 31 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the heading of the patent, lines 2 and 3 of the names of theinventors, change "Richard Graham Grosland" to --Richard GrahamCrosland-.

Signed and sealed this 25th day of January 1972.

{BEAIJ Antes? V- mm M.FLETCHER, JR. ROBERT OTTSCHALK 3 ltbesting OfficerCommissioner of Patents FORM PO'WSO USCOMM-DC suave-pea 9 U 5 GOVERNMENTPRINTING OFFICE 7959 O-'$6 334

1. Apparatus for sensing article-identifying markings constituted bycombinations of markers of two kinds, viz of magnetic and nonmagneticmaterial, carried by each article at predetermined positions torepresent a binary number, a marker of one kind representing the digit 1and a marker of the other kind representing the digit 0, said apparatuscomprising at least one electromagnetic sensing device including amagnetic circuit into which one of said markers can be placed to producean electric output governed by the reluctance of said magnetic circuit,each said sensing device including a coil coupled to the magneticcircuit, means for producing a reference voltage and means for derivingthe difference between the output from the coil and said referencevoltage as the final output voltage.
 2. Apparatus as claimed in claim 1,in which the means for producing the reference voltage comprises afurther device including a magnetic circuit having a reluctance which isalways in a condition substantially the same as that of the sensingdevice when a selected kind of marker is in its magnetic circuit. 3.Apparatus for sensing article-identifying markings constituted bycombinations of markers of two kinds, viz of magnetic and nonmagneticmaterial, carried by each article at predetermined positions torepresent a binary number, a marker of one kind representing the digit 1and a marker of the other kind representing the digit 0, said apparatuscomprising an electromagnetic sensing device including a magneticcircuit into which one of said markers can be placed to produce anelectric output governed by the reluctance of said magnetic circuit,means for moving each article past said sensing device So that themarkers therein pass into and out of the magnetic circuit of the devicein sequence to produce an output signal comprising a series of pulses ona single output line, said single output line connected to deliver saidpulses to a shift register so that after all said markers have passedinto and out of the magnetic circuit said shaft register contains astored representation of the binary number represented by said markers,said shift register being operable to read out said storedrepresentation in the serial or the parallel mode.